Meanings of a double-notch audiogram.

Audiological findings in patients with histories of noise exposure were examined. 27 patients (1.5%) were found to have audiograms with a double-notch configuration. Information from their occupational history, medical history, and audiological findings was gathered and analysed. Their results were compared with those of 50 random samples of patients without the double-notch audiogram. Analyses suggest that the low frequency notch is probably also caused by noise damage. The low incidence of double-notch audiogram reflects the small proportion of people with susceptibility to noise damage at the 500 Hz to 1 kHz region in addition to the 3 to 6 kHz region. This double-notch configuration could be exaggerated possibly by the release from inhibition by damaged hair cells.